Variously based cationic paint binders are used in their protonized, water-dilutable form especially in the electrodip painting process (CED process) for corrosion-resistant primers or decorative one-layer coatings. However, the crosslinking by amino resins or phenolic resins usual for other paint systems is not advantageous for cationic binders because of the basic character of the applied film.
In U.S. Pat. No. 2,995,531, a process is proposed for utilizing blocked polyisocyanates, which unblock at the baking or curing temperature for the crosslinking of cationic binders. According to German Patent No. 2,057,799, this method is also employed for the paint films applied by the CED process. In a large number of publications, such crosslinking components for CED binders are modified in diverse ways.
EP-A2-149,156 describes crosslinking components which are based on carbamates obtained from polyprimary amines and organic carbonates which permit urethane linkages without the use of isocyanate compounds.
With all of the known crosslinking components, however, a lowering of the baking or curing temperature is possible only if relatively large quantities of heavy metal catalysts, such as salts of tin or lead, are used. It has now been found that low baking or curing temperatures are possible if reaction products of hydroxyl-functional carbamate compounds with half-blocked diisocyanates are used as the crosslinking component.